Originally posted by Cuthbert does the K mount version allow open TTL metering or does it need to be stopped down like a "normal" M42 lens?
The K-mount version is standard Pentax-K with aperture set using the aperture ring (no base contacts). Most K-mount film cameras* are able to TTL meter, open-aperture, with the lens in M or Av modes. However, TTL metering on Pentax dSLRs and crippled-mount film bodies is done stop-down with auto aperture actuation retained in M mode.
Steve
* For the cameras on my shelf, the list includes Ricoh XR-2s, Ricoh XR7, Pentax KX, and Pentax Super Program. If the Zenit Automat were operational, it would work on it too.